1. Field of the Invention
This invention relates generally to tire sidewall architecture and more specifically, to a shear decoupling layer in the sidewall for minimizing tire damage from pinch shock.
2. Description of the Related Art
As used here, pinch shock describes a tire condition that can result when the tread section of the tire is impacted in a manner that causes the shoulder section of the tire to contact or nearly contact the bead section of the tire. In such condition, the sidewall of the tire buckles or folds over itself as the shoulder section makes or nearly makes contact with the bead section. During such pinching, the rubber mix and carcass layer of the tire composite structure are compressed between the rim and an obstacle or other feature in the travel path of the tire. Since the rubber-based materials used in the tire are virtually incompressible, the rubber expands in directions largely perpendicular to the forces causing the pinch. Such expansion is known as the Poisson effect. The rubber expansion is transferred as a displacement to the carcass layer cords and under certain conditions, such as a severe impact, the carcass layer cords may undergo a deformation beyond their rupture strength causing the cords to sever.
It has been observed that such damage from pinch shock often results in the carcass layer cords being severed in two different places—either within the shoulder section of the tire, within the bead section of the tire or both. Such severing of the cords is undesirable because the cords contribute to the structural integrity of the tire. Depending on the number of cords that are broken, the tire may show a deformation or a cut or if the damage is severe enough, a tire deflation.
In general, poor road conditions or other factors causing severe impact on the tread section of the tire can be responsible for pinch shock. For example, unpaved or poorly paved roads may have a variety of holes or other sudden changes in elevation that can lead to pinch shock. Similarly, roads containing debris or other obstructions can cause pinch shock as the tire encounters such obstacles in the road. Accordingly, for road surfaces where conditions leading to severe pinching of the tire are anticipated or expected, a tire more resistant to the breaking of radial plies is desirable.